Liquid crystal displays are widely used today in various devices and applications. Typically, a liquid crystal display includes electrodes that form an electric field upon receiving a voltage, and a layer of liquid crystal molecules that are controlled by the electric field. More specifically, the dielectric anisotropy of the liquid crystal molecules makes it possible to change the orientation of the liquid crystal molecules by controlling the electric field.
Liquid crystal molecules may tilt in response to an electric field. Uniform brightness is achieved in the end device when the liquid crystal molecules tilt in the same direction. If the liquid crystal tilt direction is not uniform, the brightness of the end device may be compromised, affecting the image quality. To avoid non-uniform brightness, a pre-tilt angle is achieved for the molecules. The pre-tilt angle typically falls within a given range. If the pre-tilt angle is too high, the birefringence due to the pre-tilt of the molecules will cause a light leakage in the dark state, reducing contrast ratio. If the pre-tilt angle is too low (e.g., less than 0.5 degrees), the molecules may tilt in diametrically opposite directions when a voltage is suddenly applied.
A desired pre-tilt may be achieved by a number of methods, such as oblique photoalignment. Oblique photoalignment sets the alignment direction and angle of liquid crystal molecules by irradiating an alignment layer at an oblique angle with light that is polarized perpendicularly to the direction of the beam. The oblique photoalignment technique, however, has drawbacks due to the unconventional geometry of the optical setup and the photolithography that cause problems such as nonuniform light intensity, shadow effects by patterning masks, and surface roughness.
A method of achieving uniform pre-tilt in liquid crystal molecules is desired.